82 BULLETIN 126, U. S. DEPARTMENT OF AGRICULTURE. 



The lining has a 3^-inch base overlaid with a Jr-inch top coating of 

 cement mortar hand-troweled to a very smooth and even surface. 

 The canal has a bottom width of 10 feet, 1^ to 1 side slopes, and a 

 vertical depth of 6^ feet. At the top of the lining a 1-foot berm 

 extends back into the bank. When carrying a 6-foot depth of water 

 the canal has a capacity of 615 second-feet. 



The lined portion of this canal offers an example of unusual care in 

 construction to obtain a smooth interior. Its curves have been spi- 

 raled throughout. The lining is made up of 16-foot sections on tan- 

 gents and 12-foot sections on curves. The exact shape of the finished 

 section was secured by the use of a template having the same area as 

 the cross section of the finished canal. The methods employed in 

 construction and various details of the work are shown in Plates XV 

 to XVII, inclusive. The concrete was laid continuously. Adjoin- 

 ing slabs were separated by one thickness of tar paper and connected 

 by short lengths of ^-inch steel rods used as dowel pins. The entire 

 surface of the lining was plastered and smoothed with a steel trowel 

 as soon as the concrete had set sufficiently to permit it, and which 

 doubtless accounts for the absence of surface scaling. 



No displacements due to pressure, settlement, or buckling are to be 

 found in this lining. The only cracks which have appeared are those 

 at the expansion joints. It has been noticed that in the summer 

 these, found to be about 0.025 to 0.030 inch wide in the morning, 

 are tightly closed by 1 or 2 o'clock in the afternoon. 



A brief summary of data on various canal linings is given in Table 

 IV for the purpose of supplementing that contained in the text 



